docs: def credentials_required(method_func):
      """
      Decorator for methods that checks that the client has credentials.
  
      Throws a CredentialsMissingError when they are absent.
      """
      def _checkcredentials(self, *args, **kwargs):
          if self.username and self.password:
              return method_func(self, *args, **kwargs)
          else:
              raise CredentialsMissingError("This is a private method. \
  You must provide a username and password when you initialize the \
  DocumentCloud client to attempt this type of request.")
  
      return wraps(method_func)(_checkcredentials)